Can you control how an SVG s stroke-width is drawn

Question

Currently building a browser-based SVG application  Within this app  various shapes can be styled and positioned by the user  including rectangles   When I apply a stroke-width to an SVG rect element of say 1px  the stroke is applied to the rect   s offset and inset in different ways by different browsers  This is proving to be troublesome  especially when I try to calculate the outer width and visual position of a rectangle and position it next to other elements    For example    Firefox adds 1px inset  bottom and left   and 1px offset  top and right  Chrome adds 1px inset  top and left   and 1px offset  bottom and right    My only solution so far would be to draw the actual borders myself  probably with the path tool  and position the borders behind the stroked element  But this solution is an unpleasant workaround  and I   d prefer not to go down this road if possible   So my question is  can you control how an SVG   s stroke-width is drawn on elements

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As people above have noted you ll either have to recalculate an offset to the stroke s path coordinates or double its width and then mask one side or the other  because not only does SVG not natively support Illustrator s stroke alignment  but PostScript doesn t either    The specification for strokes in Adobe s PostScript Manual 2nd edition states   4 5 1 Stroking  The stroke operator draws a line of some thickness along the current path  For each straight or curved segment in the path  stroke draws a line that is centered on the segment with sides parallel to the segment    emphasis theirs   The rest of the specification has no attributes for offsetting the line s position  When Illustrator lets you align inside or outside  it s recalculating the actual path s offset  because it s still computationally cheaper than overprinting then masking   The path coordinates in the  ai document are reference  not what gets rastered or exported to a final format    Because Inkscape s native format is spec SVG  it can t offer a feature the spec lacks

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A  dirty  possible solution is by using patterns   here is an example with an inside stroked triangle    https   jsfiddle net qr3p7php 5    lt style gt   triangle1    fill   0F0    fill-opacity  0 3    stroke   000    stroke-opacity  0 5    stroke-width  20     triangle2    stroke   f00    stroke-opacity  1    stroke-width  1         lt  style gt    lt svg height  210  width  400   gt       lt pattern id  fagl  patternUnits  objectBoundingBox  width  2  height  1  x  -50   gt           lt path id  triangle1  d  M150 0 L75 200 L225 200 Z  gt       lt  pattern gt           lt path id  triangle2  d  M150 0 L75 200 L225 200 Z  fill  url  fagl    gt   lt  svg gt

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UPDATE  The stroke-alignment attribute was on April 1st  2015 moved to a completely new spec called SVG Strokes  As of the SVG 2 0 Editor   s Draft of February 26th  2015  and possibly since February 13th   the stroke-alignment property is present with the values inner  center  default  and outer  It seems to work the same way as the stroke-location property proposed by  Phrogz and the later stroke-position suggestion  This property has been planned since at least 2011  but apart from an annotation that said  SVG 2 shall include a way to specify stroke position    it has never been detailed in the spec as it was deferred - until now  it seems  No browser support this property  or  as far as I know  any of the new SVG 2 features  yet  but hopefully they will soon as the spec matures  This has been a property I personally have been urging to have  and I m really happy that it s finally there in the spec  There seems to be some issues as to how to the property should behave on open paths as well as loops  These issues will  most probably  prolong implementations across browsers  However  I will update this answer with new information as browsers begin to support this property

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I found an easy way  which has a few restrictions  but worked for me    define the shape in defs define a clip path referencing the shape use it and double the stroke with as the outside is clipped   Here a working example    x000D   x000D   lt svg width  240  height  240  viewBox  0 0 1024 1024  gt  x000D   lt defs gt  x000D    lt path id  ld  d  M256 0 L0 512 L384 512 L128 1024 L1024 384 L640 384 L896 0 L256 0 Z   gt  x000D    lt clipPath id  clip  gt  x000D     lt use xlink href   ld   gt  x000D    lt  clipPath gt  x000D   lt  defs gt  x000D   lt g gt  x000D    lt use xlink href   ld  stroke   0081C6  stroke-width  160  fill   00D2B8  clip-path  url  clip    gt  x000D   lt  g gt  x000D   lt  svg gt  x000D   x000D   x000D

User · Answer

No  you cannot specify whether the stroke is drawn inside or outside an element  I made a proposal to the SVG working group for this functionality in 2003  but it received no support  or discussion      As I noted in the proposal    you can achieve the same visual result as  inside  by doubling your stroke width and then using a clipping path to clip the object to itself  and you can achieve the same visual result as  outside  by doubling the stroke width and then overlaying a no-stroke copy of the object on top of itself    Edit  This answer may be wrong in the future  It should be possible to achieve these results using SVG Vector Effects  by combining veStrokePath with veIntersect  for  inside   or with veExclude  for  outside   However  Vector Effects are still a working draft module with no implementations that I can yet find   Edit 2  The SVG 2 draft specification includes a stroke-alignment property  with center inside outside possible  values   This property may make it into UAs eventually   Edit 3  Amusingly and dissapointingly  the SVG working group has removed stroke-alignment from SVG 2  You can see some of the concerns described after the prose here

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Here is a work around for inner bordered rect using symbol and use   Example  https   jsbin com yopemiwame edit html output  SVG    lt svg gt     lt symbol id  inner-border-rect  gt       lt rect class  inner-border  width  100   height  100   style  fill rgb 0 255 255  stroke-width 10 stroke rgb 0 0 0   gt     lt  symbol gt           lt use xlink href   inner-border-rect  x     y     width     height     gt   lt  svg gt    Note  Make sure to replace the   in use with real values   Background  The reason why this works is because symbol establishes a new viewport by replacing symbol with svg and creating an element in the shadow DOM  This svg of the shadow DOM is then linked into your current SVG element  Note that svgs can be nested and every svg creates a new viewport  which clips everything that overlaps  including the overlapping border  For a much more detailed overview of whats going on read this fantastic article by Sara Soueidan

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Here s a function that will calculate how many pixels you need to add - using the given stroke - to the top  right  bottom and left  all based on the browser   var getStrokeOffsets   function stroke            var strokeFloor         Math floor stroke   2                                                                      max offset             strokeCeil          Math ceil stroke   2                                                                       min offset          if   browser mozilla                                                                                               Mozilla offsets              return                   bottom      strokeFloor                  left        strokeFloor                  top         strokeCeil                  right       strokeCeil                          else if   browser webkit                                                                                          WebKit offsets              return                   bottom      strokeCeil                  left        strokeFloor                  top         strokeFloor                  right       strokeCeil                          else                                                                                                              default offsets              return                   bottom      strokeCeil                  left        strokeCeil                  top         strokeCeil                  right       strokeCeil

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I don   t know how helpful will that be but in my case I just created another circle with border only and placed it    inside    the other shape

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The solution from Xavier Ho of doubling the width of the stroke and changing the paint-order is brilliant  although only works if the fill is a solid color  with no transparency   I have developed other approach  more complicated but works for any fill  It also works in ellipses or paths  with the later there are some corner cases with strange behaviour  for example open paths that crosses theirselves  but not much    The trick is to display the shape in two layers  One without stroke  only fill   and another one only with stroke at double width  transparent fill  and passed through a mask that shows the whole shape  but hides the original shape without stroke      lt svg width  240  height  240  viewBox  0 0 1024 1024  gt     lt defs gt       lt path id  ld  d  M256 0 L0 512 L384 512 L128 1024 L1024 384 L640 384 L896 0 L256 0 Z   gt       lt mask id  mask  gt         lt use xlink href   ld  stroke   FFFFFF  stroke-width  160  fill   FFFFFF   gt         lt use xlink href   ld  fill   000000   gt       lt  mask gt     lt  defs gt     lt g gt       lt use xlink href   ld  fill   00D2B8   gt       lt use xlink href   ld  stroke   0081C6  stroke-width  160  fill  red  mask  url  mask    gt     lt  g gt     lt  svg gt

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You can use CSS to style the order of stroke and fills  That is  stroke first and then fill second  and get the desired effect   MDN on paint-order  https   developer mozilla org en-US docs Web SVG Attribute paint-order  CSS code   paint-order  stroke

[svg] Can you control how an SVG's stroke-width is drawn?

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